j0089184.wmf (7164 bytes)Disk Drives

In the early days of computing, information storage was done on magnetic tape, similar to VCR or cassette tape.  The disadvantage of using tape as a storage device was that it could not be accessed randomly.  In other words, if information was stored midway on the tape, the tape would have to be forwarded or rewound to that position before the information could be retrieved.  The first Radio Shack TRS-80's could have a cassette tape player hooked to them and could then store information.  It was necessary for the user to write down the tape recorder's counter position whenever a new set of data was stored. 

This primitive means of storing and retrieving data was soon replaced by the 5.25-inch floppy disk.  The wonderful thing about this disk was that the computer itself kept track of where the information was stored and could access information from anywhere on the disk very rapidly.  The large floppy disk (named because of its flexibility) was replaced by the 3.5-inch plastic shielded diskette which proved to be more durable and small enough to fit in a shirt pocket.  The large floppy disk could hold about 360 KB of information while the diskette could hold up to 1.44 MB.  New diskette drive designs (called Superdrives) allow as much as 120 MB of storage on a single disk!

The workhorse of the modern PC is the hard disk drive (HDD).  A hard disk drive consists of a set of stacked metal platters coated on both sides with a magnetic recording material.  The platters are read by magnetic reading heads, each resembling the tone-arm of a record player.  The more platters and reading heads built into the drive, the larger the storage capacity.  The HDD stores the operating instructions needed by the computer to start up and run properly.  It is vital to keep the HDD working properly in order for the computer to remain healthy.   The dreaded "Computer Crash" normally occurs whenever the hard disk drive fails to work.  Maintaining the integrity of data on a HDD has become an industry in itself. 

Computers can have more than one HDD and more than one diskette drive.  The HDD is normally referred to as the "C: Drive" while the diskette drive is commonly referred to as the "A: Drive".  A second diskette drive is usually designated as the "B: Drive".  Additional hard disk drives will be given different drive labels, such as "F: Drive", "G: Drive", etc.  On a network, other storage devices can be "mapped" and used as storage devices by the local computer.  These drives will also be assigned letters. 

Other drives attached to the computer (such as CD-ROM Drives, Zip Drives, Jaz Drives and SCSI Drives) are assigned additional drive letters so that the computer operator and the computer can keep track of where the data will be coming from or going to.   The more complex the machine, the more complex its maintenance.